The description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The need for energy-efficient or green communication solutions is inevitably increasing (Y. Chen, S. Zhang, S. Xu, and G. Y. Li, “Fundamental trade-offs on green wireless networks,” Commun. Mag. IEEE, vol. 49, no. 6, pp. 30-37, 2011, incorporated herein by reference). Femtocells have been proposed as an energy-efficient solution, which enhance coverage and data rates in addition to maintaining the energy consumption of mobile sets and macrocells at a reasonable level. What makes femtocells an energy efficient technology is the reduction in the distance between the indoor users. This enables the base station to multitask more efficiently and also helps the macrocell to focus on outdoors mobile users (V. Chandrasekhar, J. Andrews, and A. Gatherer, “Femtocell networks: a survey,” Commun. Mag. IEEE, vol. 46, no. 9, pp. 59-67, 2008, incorporated herein by reference).
Another technology that can be used to increase the energy and spectrum efficiency of wireless networks is the use of cognitive radio (D. Grace, J. Chen, T. Jiang, and P. D. Mitchell, “Using cognitive radio to deliver ‘Green’ communications,” in Cognitive Radio Oriented Wireless Networks and Communications, 2009. CROWNCOM '09.4th International Conference on cognitive radio wireless networks, 2009, pp. 1-6, incorporated herein by reference).
A cognitive radio is an intelligent radio that can be programmed and configured dynamically. It can be a self-organized radio which has the ability to change its operating frequency according to the changes in the surrounding environment, and by doing so, it exploits the spectrum holes to increase its choices of bandwidth (S. Haykin, “Fundamental Issues in Cognitive Radio,” in Cognitive Wireless Communication Networks, E. Hossain and V. Bhargava, Eds. Springer US, 2007, pp. 1-43, incorporated herein by reference). One such way that cognitive radios can be effective with regard to bandwidth choices is that by increasing the bandwidth, the energy usage can be decreased because network capacity increases linearly with bandwidth and logarithmically with power (D. Grace, J. Chen, T. Jiang, and P. D. Mitchell, “Using cognitive radio to deliver ‘Green’ communications,” in Cognitive Radio Oriented Wireless Networks and Communications, 2009. CROWNCOM '09. 4th International Conference on cognitive radio wireless networks, 2009, pp. 1-6, incorporated herein by reference).